Provide a ready-to-go default configuration

These changes aim to provide a simple setup to get a developer started on exploring Kibana.

 * adds two README examples and a basic Nginx server-config.
 * disables Basic Auth protection for ES endpoints, but keeps examples as code comment
 * sets default for `config["elasticsearch"]` to `window.location.origin`

This allows to install Kibana to an ES host as a site-plugin via the `plugin` command's Github integration:

        plugin install elasticsearch/kibana